1. Field of the Invention
This invention relates to a method of controlling a plurality of regulated converters or switching regulators operating in parallel and, more particularly, to a system including paralleled converters being controlled by a central regulation circuit and providing protection against a failure of the central regulation circuit while leaving the individual converters fully operative.
2. Description of the Prior Art
Regulated converters, which operate as a current source, may be readily paralleled since they permit load sharing among a plurality of paralleled converters. Paralleling of current source-type converters is discussed in an article by C. W. Deisch entitled "Simple Switching Control Method Changes Power Converter Into A Current Source" published in the IEEE Power Electronics Specialist Conference Proceedings of 1978 pages 300 through 306. Deisch, whose teachings are incorporated herein, discloses a current source-type of converter which has a voltage regulated output. In a current source-type converter with voltage regulation, the output voltage is monitored and compared with a reference voltage to generate an error voltage signal. This error voltage signal is used as the basis for a control voltage. Current flow through the converter switching device is monitored, and a voltage waveform proportional to the detected current is continuously compared with the control voltage derived from the error voltage. The converter switching device is regularly biased conducting by a constant frequency clock. This causes the current to begin increasing with time. When the current voltage waveform equals the control voltage, the switching device is biased nonconducting. The current then begins to decrease until the clock biases the switching device conducting again and the cycle is repeated.
In the paralleled system of converters disclosed by Deisch, a plurality of current source-type converters is connected to a common load. The voltage at that common load is monitored and compared with a reference voltage by a central regulation circuit which generates a voltage error signal. This single error signal is applied in common to each of the paralleled current source-type converters and is used in each individual converter as a regulation control voltage, to control the peak current flowing through the switching device of that converter. It should be noted that the average output current of the converter is approximately equal to the peak current.
It is readily apparent to those skilled in the art that this foregoing scheme of regulation results in the sharing of the load current between the various converters; however, it is just as apparent that the use of a single central voltage regulation control circuit operative to supply a common control voltage to each of the paralleled converters compromises the reliability of the entire power supply system. This is especially important in applications where a separate converter is provided for redundancy purposes to assure high reliability by automatically compensating for a single converter failure. A single failure of the central regulation control circuit causes a failure of the entire system.